The present invention relates generally to a light guide for transmitting and/or distributing light. More particularly, the present invention relates to a light guide that transports light by total internal reflection.
Light guides (i.e., light pipes, light conduits or light tubes) are commonly used to transmit light from a light source (e.g., a high intensity bulb) to a remote location with relatively low transmission losses. Light guides can also be used to effectively distribute decorative or functional light over relatively large areas.
A common light guide construction includes a tubular wall having an inner non-structured side, and an outer structured side. The non-structured side is generally smooth, while the structured side conventionally includes a linear array of prisms arranged side-by-side in parallel relationship to form a plurality of triangular grooves running the length of the light guide. Light entering the light guide within an acceptable angular range is contained by total internal reflection as it travels along the length of the light guide. An exemplary light guide, as described above, is disclosed in U.S. Pat. No. 4,805,984, which is hereby incorporated by reference.
Various techniques have been used to distribute light from a light guide for the purpose of illuminating an area. One technique involves altering the prisms (e.g., by rounding the prism corners, abrading the prisms, completely removing selected prisms, etc.) such that light is released through the altered regions. Another technique involves placing a light extractor within the light guide. Typically, the extractor is a strip or sheet of material (e.g., xe2x80x9cSCOTCH-CAL EXTRACTOR FILM(trademark)xe2x80x9d) configured to reflect the light toward the light guide wall at an angle outside the angular range of total internal reflection. When the light is reflected in such a manner, the internal reflectance of the light guide is reduced, thereby allowing light to escape through the wall of the guide to provide decorative or functional lighting.
Light guides are commonly manufactured using optical lighting film (OLF). A typical OLF is made of a relatively thin sheet of transparent material (e.g., acrylic or polycarbonate) having a linear array of prisms embossed or otherwise formed at one side of the sheet. The sheet of material is typically sufficiently flexible to allow the OLF to be rolled to form a light guide in the form of a tube. OLF""s suitable for use in manufacturing light guides are disclosed in U.S. Pat. Nos. 4,906,070 and 5,056,892, which are hereby incorporated by reference.
One aspect of the present invention relates to a light conveying device including a hollow light guide. The light guide includes a wall having a generally smooth inner side and a structured outer side. The structured outer side includes a plurality of prisms defining grooves that extend along a length of the light guide. A protective outer sleeve is provided around the structured outer side of the light guide. In certain embodiments, the sleeve is bonded to the light guide at least three locations spaced about a perimeter of the light guide. In other embodiments, a fixture is used to retain the light guide in an elastically deformed, non-cylindrical cross-sectional configuration.